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1998 (US) 740il purchased mid last year (June-July) with 55,000 miles. A week ago, under spirited acceleration while merging onto a local highway, the upper radiator hose blew off of it. Very cold outside, so I had a bit of time to get to a parking lot before the engine went way too hot. Discovered that the upper radiator hose had the ribbed section of the plastic radiator port stuck in it an inch or two from the radiator main housing. Removed the broken piece of the "radiator" from the hose, refitted the hose, in a temporary fashion, filled system with H2O and limped home. Going to replace/ordered the radiator, clamps, hoses, expansion tank, cap, bleeder screw, along with a new serpentine belt. Just thought to share with my fellow enthusiasts. Any comments welcome.
p.s Already replaced the CPS, which was about 97% of another problem that, upon further review, I'm pretty sure replacing the "PCV" valve will clear up. My thanks to all for the info contained herein the forum. A lifesaver for me.

These babies run hot. Any weak point will be exploited. I blew a hose at the rear firewall after a long trip to Florida. Was thankful it happened once I was there instead of on the highway. Read of many cooling issues on the E38. Now home I decided how much I like the car and want to use it more often. Not wanting anything on my mind I ordered every hose on the engine and a new heater valve also. When those clog hoses explode! I also bought a new radiator online pretty cheap. VERY important to bleed thoroughly. The mechanic in Fla. felt I wasn't bled correctly and this led to extra pressure on a weak hose. So after I install all new, I will make sure I am bled correctly. I am installing a new fan blade have read of those breaking apart causing damage also. They get brittle. Good luck!!!

Yes, sounds like a heater hose blew out on you? I'll be sure to check all the hoses, and maybe replace that fan blade too. Thanks to your friendly reminder. That's the thing with "not new/near new" cars is all the "wear items" do just that. I'm absolutely sure the lady doctor I bought the car from never pushed the throttle very hard. So now all the stuff that is questionable is coming to light. But it's cool, all family/friends/me especially love the car. The first BMW I bought in the early 2000's was a hi mileage '95 540i. That was a car that did everything well. So, when it got almost 300,000 miles on it, picked up the very low mileage '98 740il. Thanks for the reply/info!

Hey i was wondering if you ever found a reason for this problem, yesterday i was driving and just randomly i noticed steam coming from under my hood, i pulled over to check it and it was just my hose had popped off i didnt think it was that big of a deal so i just put it back in and retightened it and refilled with coolant but now its an ongoing issue im limited funds or id bring her to a mechanic

Hoses wear out in a few different ways, and when they do you just replace them. As long as nothing actually broke off your radiator that's my suggestion. And use a new hose clamp.

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Before...
After...(this may take a few years, it's my DD and I have bigger projects)

2005 Venture Extended LT - what else you gonna drive when you have 6 kids, cargo and still want better than 10MPG
2000 Impala LS - because you need something to beat the snot out of in a Michigan winter
1999 BMW 740i - why do I have Chevys again?
2001 BMW 330xi - father/son project time!

Yes, my problem was that the plastic upper radiator hose port that the upper radiator hose connects to, had cracked off inside the upper radiator hose. I had done some passing on the highway just prior to the hose "blowing off." I then saw a puff of water/vapor coming from the left front grill area airborne coming by the left side (driver) outside rear view mirror. Along with the smell of warm ethylene glycol anti-freeze coolant. I'd figured the plastic radiator port the radiator hose connects to, was just old. (and plastic) So, I replaced the radiator unit and the affected associated parts. Hoses and clamps. Autohouse AZ discount parts...been working just fine to date. No problems since. (knock on wood?) Hope things go well for you.